The present disclosure relates to back electromotive force phase detection and excitation control for a stepper motor. More particularly, the present invention relates to back electromotive force phase detection and excitation control for a two-phase excitation stepper motor that is operated by constant-current PWM drive.
Stepper motors are generally driven by an open-loop control. Therefore, if a drive current is insufficient (i.e., drive torque is insufficient), then the stepper motor immediately falls out of synchronization. Therefore, an excessive amount of drive current is supplied to the stepper motor so as to secure a sufficient drive torque margin to overcome any load torque.
In order to reduce the power consumption of the stepper motor, it is necessary to detect a sign that the stepper motor will fall out of synchronization during an increase in load torque that occurs suddenly, and increase a drive current as required. Conventionally, an angle deviation that is a difference between a drive current phase and a back electromotive force phase is calculated based on the result of detection by a detector for monitoring the status of motor drive, such as a position sensor, an acceleration sensor or the like, and based on the angle deviation, a sign that the stepper motor will fall out of synchronization is detected.